Water injection in Ekofisk Field (2/4K) in the Norwegian sector of the North Sea has started late 1987. The waterflood was decided on after the success of a pilot water flood trial initiated in the spring of 1981. Ekofisk reservoir is described as a fine-grained chalky limestone with porosities frequently above 40% and a matrix permeability of only 1 to 2 md. However, a fracture system raises overall permeability to about 100 md.

An important factor in the success of a waterflood project is the quality of the water required for injection into the reservoir. The water quality is greatly affected by several contaminants such as corrosion products/suspended solids, scale and bacteria.

Controling corrosion and minimizing solids generation are two major problems associated with the waterflood. The two problems are related since the solids picked up are corrosion products and/or biomass that cause corrosion. Microbial corrosion may be eleminated/ minimized by frequent treatment with bactericides. The treatment frequency depends on the bactericidal demands and type of bactericide. These, interns are related to the bacterial activities, hence dependent on the monitoring techniques for bacteria counts.

Monitoring of microbial corrosion is always difficult due to the sessile nature of bacteria and the lack of meaningful correlation between bacteria counts and the bacterial activity.

The water injection system on 2/4K is considered to be a unique system since continuous disinfiction of the injected water by UV sterilization technique is used.

Experience gained from the use of the UV sterilization, the bactericidal treatment regime and a comparison between various monitoring techniques of the bacteria are discussed in this pacer.

You can access this article if you purchase or spend a download.